The World's Slowest Experiment: Nearly a Century of Observation at the University of Queensland

The Pitch Drop Experiment: A Century of Patience

In a quiet corner of the University of Queensland in Australia, an experiment that began in 1927 is still ongoing, making it one of the longest-running laboratory experiments in the world. Known as the Pitch Drop Experiment, it was set up by Professor Thomas Parnell to demonstrate that pitch—a derivative of tar once used in roofing and waterproofing—is actually a liquid, albeit an extraordinarily viscous one. The experiment consists of a funnel containing a sample of heated pitch, which was allowed to cool and solidify. The funnel was then cut at the stem, and the pitch began to drip—very, very slowly.

How the Experiment Works

The pitch in the funnel is a viscoelastic material that flows like a liquid over long timescales but behaves like a solid under short-term stress. The experiment measures the time between drops. Since the funnel was cut in 1930, only nine drops have fallen. The most recent drop occurred in April 2014, and the next one is expected sometime in the 2020s. The rate of dripping has been remarkably consistent, with an average interval of about nine years per drop, though the exact timing varies due to temperature fluctuations in the laboratory.

Scientific Significance

While the experiment may seem like a curiosity, it has provided valuable data on the viscosity of pitch. The measured viscosity is about 230 billion times that of water, making pitch one of the most viscous known liquids. This has implications for understanding the flow of materials in geophysics, such as the movement of glaciers and the deformation of rocks over geological timescales. The experiment also serves as a powerful educational tool, demonstrating the concept of supercooled liquids and the importance of long-term observation in science.

Challenges and Preservation

Maintaining the experiment for nearly a century has not been without challenges. The original funnel was protected by a glass case, but the laboratory has moved several times. The experiment has survived World War II, changes in university leadership, and even a brief period when it was nearly forgotten. Today, it is carefully monitored by a team of researchers who ensure that the temperature and humidity remain stable. A webcam now streams the experiment live, allowing scientists and the public to watch for the next drop.

Comparison with Other Long-Term Experiments

The Pitch Drop Experiment is often compared to other long-running studies, such as the Beverly Clock at the University of Otago in New Zealand, which has been running since 1864 without winding, and the Oxford Electric Bell, which has been ringing since 1840. However, the Pitch Drop Experiment is unique in that it measures a physical property of a material over an extended period, rather than simply demonstrating a mechanism. It has inspired similar experiments worldwide, including one at Trinity College Dublin that began in 1944.

Cultural Impact

The experiment has captured the public imagination, earning the nickname "the world's slowest experiment." It has been featured in numerous documentaries and articles, and it even won an Ig Nobel Prize in 2005 for "patience in science." The experiment's longevity and simplicity remind us that some scientific questions require decades of careful observation to answer.

Future of the Experiment

As the next drop approaches, researchers are preparing to capture it in high definition. The experiment is expected to continue for many more decades, potentially outlasting its current custodians. Plans are in place to ensure that the experiment remains undisturbed, with detailed protocols for future generations of scientists. The Pitch Drop Experiment stands as a testament to the value of long-term scientific inquiry and the patience required to unlock nature's secrets.

This article is based on reporting by Interesting Engineering. Read the original article.